If they sell XP licenses then they can't boast about how many copies of the latest version of Windows has been sold to try and get people to hop on the bandwagon when, in fact, the majority of those purchases weren't to use the latest version at all. They have been trying to pull the same tactic with Vista to try and convince people that Vista is infinitely better than XP.

With RAID 10 you still can have 2 drives fail and lose all your data. Though if you're lucky you'll have the second failure on the same side of the mirrored portion in which case you'll still have your data.